The invention relates to a disc brake, in particular for a motor vehicle, comprising a bidirectional wear adjustment device coupled to a brake application device, as well as to the bidirectional wear adjustment device.
Vehicles and certain technical equipment often use friction brakes to convert kinetic energy. Disc brakes are preferred here, especially in the passenger car and commercial vehicle sectors. With the typical design of a disc brake, said disc brake comprises a brake caliper together with an internal mechanism, generally comprising two brake pads and the brake disc. Brake cylinder forces are introduced into the internal mechanism via a pneumatically actuated cylinder, are multiplied by an eccentric mechanism, and are transmitted as a brake application force to the brake pads and the brake disc via threaded tubes, which are also referred to as threaded plungers or threaded spindles, with the wear on the brake disc and the brake pads being compensated by way of the threaded tubes.
The brake application forces act via both brake pads on the brake disc, which undergoes retardation of the rotary motion depending on the level of the brake application force. A clearance between the brake pads and the brake disc is referred to as a release clearance (or gap). The retardation is significantly affected by the friction coefficient between the brake disc and the brake pad. Since the pads are designed as parts that wear out and the friction coefficients are dependent on rigidity, these pads are generally softer than the brake disc, i.e. the pads undergo a change in pad thickness over their time in use: they wear. Owing to this pad wear and additional disc wear, said release clearance increases. This change in pad thickness gives rise to the need for wear adjustment to compensate for the change and thus establish a constant release clearance.
One example of an adjustment device is described in DE 10 2004 037 771 A1. Here, a rotary driving motion is transmitted to an adjusting spindle of a plunger, e.g. by a torque limiting device, having a ball ramp for example, via a continuously acting clutch (slipping clutch). Here, the release clearance is adjusted continuously.
Bidirectionally acting brake release clearance adjusting arrangements are furthermore known in various embodiments, e.g. electric-motor-driven and electronically controlled adjustment devices, which can increase and reduce a brake release clearance as desired and act only in nonbraking phases. One example that may be mentioned for illustration purposes is DE 197 31 696.
Examples of mechanically driven and mechanically acting combined adjustment and return devices which can increase and reduce the release clearance in steps during brake actuations are described by DE 10 2012 012 473 and DE 10 2012 102 577, for example.
Other mechanically driven and mechanically acting adjustment devices can reduce an enlarged release clearance during brake actuations. In the case of an unwanted reduction in the release clearance below the desired value, they exploit existing return rotation effects on the actuating spindles in order to increase the release clearance in very small steps. When the desired value is reached, further reverse rotation movement is stopped by the locking effect of the adjuster. This effect is potentially included in all known mechanically acting adjustment systems but is generally suppressed by high holding friction torques at the adjuster and/or at the spindle system in order to avoid unwanted changes in the release clearance, e.g. due to the effects of vibration.
In contrast to the bidirectional adjuster concepts described above, reductions in the release clearance occurring spontaneously in the last example can only be eliminated with a very large number of brake actuations. Such spontaneously occurring reductions in release clearance can be brought about by the following events, for example: severe vibrational stress occurring between two braking operations, incorrect release clearance adjustment, high-energy braking operations with a large increase in thickness of the brake disc and the brake pads, etc.
The object of the present invention consists in providing an improved disc brake having a bidirectional wear adjustment device.
Another object is to provide an improved wear adjustment device.
These and other objects are achieved according to the invention by a disc brake, preferably pneumatic, in particular for a motor vehicle, including a brake application device, preferably with a pivoted brake lever, at least one spindle unit having at least one threaded tube with an external thread cooperating with an internal thread of a bridge, and at least one bidirectional wear adjustment device, which is coupled to the brake application device, preferably to the pivoted brake lever. The bidirectional wear adjustment device includes an adjusting arrangement and at least one preloading arrangement, wherein the preloading arrangement is designed to influence a flank position of a thread pairing of the external thread of the at least one threaded tube and the associated internal thread of the bridge.
As compared with the prior art, the disc brake according to the invention with the bidirectional wear adjustment device has the advantage that an increased return speed of the bidirectional wear adjustment device and improved resistance to wear and the effect of vibration are provided.
Another advantage is that an already existing adjusting arrangement can be used. The reverse rotary motion of the threaded tubes is made possible and vibration resistance which is still adequate is ensured.
In one embodiment, the at least one preloading arrangement is designed to adjust a flank position of the external thread of the at least one threaded tube and of the associated internal thread of the bridge from a rest position in a state of release of the disc brake into a reverse rotation position with a reduced reverse rotation resistance of the thread pairing of the external thread of the at least one threaded tube and of the associated internal thread of the bridge during an application process of the disc brake. In this way, a reliable holding effect for the thread pairing in the rest position can be ensured, while reverse rotation resistance in the reverse rotation position can simultaneously be reduced.
The rest position should be taken to mean the position or location of the disc brake in which the disc brake is not actuated, i.e. is released. In the rest position, a center line of an internal thread of the bridge and a threaded tube axis of the threaded tube associated with said internal thread are spaced apart. That is to say, on one longitudinal side, the thread flanks of the thread pairing are backlash-free in a contact region and, on the opposite longitudinal side, there is the full thread backlash of the thread pairing.
The reverse rotation position is the position which is adopted by the at least one threaded tube when the disc brake is actuated until the brake pads rest against the brake disc, in other words during an application process of the disc brake. During this process, the center line of the internal thread of the bridge and the threaded tube axis of the threaded tube associated with said internal thread come into a position in which they coincide.
In another embodiment, the at least one preloading arrangement is designed to produce a preloading force, which acts radially on the at least one threaded tube. In tests, it has surprisingly been found that a transverse displacement of a rotatable cylindrical body which rests by means of a friction surface on a bearing surface reduces the frictional resistance of the friction surface on the bearing surface at a given axial force.
It is advantageous here if the radially acting preloading force is an elastically acting preloading force. For this purpose, the at least one preloading arrangement for producing the radially acting preloading force can have at least one energy storage element, e.g. a compression spring. Other energy storage elements are, of course, also possible, e.g. pneumatic, hydraulic, electromagnetic energy storage elements. It is particularly advantageous here if these energy storage elements are controllable, e.g. controllable gas pressure springs.
In another embodiment, the at least one preloading arrangement has at least one release mechanism, which is designed to reduce the reverse rotation resistance or holding forces of the thread pairing of the external thread of the at least one threaded tube and of the associated internal thread of the bridge during an application process of the disc brake in the reverse rotation position. Controllable adjustment of the rest position and the reverse rotation position is thereby possible. For example, two preloading arrangements arranged opposite one another can be used, wherein the first preloading arrangement is active for the adoption of the rest position. For the adoption of the reverse rotation position, the other preloading arrangement is activated and cancels out the effect of the force of the first preloading arrangement to such an extent that adoption of the reverse rotation position is ensured.
In this phase of the radially inward sliding of the threaded tube due to the slope of the thread flanks, the friction at the thread flanks in a tangential direction is also overcome, as a result of which the reverse rotation torque brought about by the thread slope by means of the loading force which builds up overcomes the frictional resistance and brings about a reverse rotation of the threaded tube during the radial sliding phase of said tube.
In yet another embodiment, the adjusting arrangement has a selector fork connected to a driving element, wherein the selector fork is provided for interaction with an actuator of the brake application device, preferably with the pivoted brake lever. The selector fork and the actuator thus form a stop for the resetting of the release clearance to the desired value of the design release clearance, which can be mechanically defined by the selector fork.
In another embodiment, the adjusting arrangement has a freewheeling and overload clutch arrangement, which interacts with the driving element. This ensures that the operation of the adjusting arrangement for adjusting the release clearance is maintained.
In yet another embodiment, the adjusting arrangement is inserted into the at least one threaded tube of the at least one spindle unit, thus saving space. Here, the adjusting arrangement is accommodated without backlash by means of its output toothing in an internal tooth profile of the associated threaded tube (separation of sleeve and star). Reliable transmission of the reverse rotary motion of the threaded tubes to the adjusting arrangement is thereby made possible.
In another embodiment, the adjusting arrangement has an optimized head friction torque, thereby making resetting easier. At the same time, high robustness and vibration stability are ensured.
A bidirectional wear adjustment device comprising an adjusting arrangement and at least one preloading arrangement is provided by the disc brake described above.
One particular advantage is that, with an appropriate flank angle α of the threaded tubes, a high holding torque is achieved at the threaded tubes with a relatively low radial stress in the rest position, and this holding torque is automatically eliminated by a “flank sliding effect” when the disc brake is actuated.
Another advantage is that the threaded tubes are held in a stable position in the rest position by the lateral pressure of the external threads of the threaded tube against the respective internal thread of the bridge, even under severe vibrational loading, and thus relative movements of the external threads of the threaded tubes with respect to the internal thread of the bridge, which can be the cause of unwanted changes in the release clearance, are avoided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.